Sparking plug electrodes



J y 18, 1967 J. F. w. BROWN ETAL 3,331,635

SPARRING PLUG ELECTRODES Filed Aug. 4, 1966 United States Patent 3,331,685 SPARKING PLUG ELECTRODES John Frederick Walter Brown, Coulsdon, Michael Eugene Cronin, London, and Joseph Aidan Stevenson, Orpington, England, assignors to Johnson, Matthey & Co. Limited, London, England, a British company Filed Aug. 4, 1966, Ser. No. 570,275 Claims priority, application Great Britain, Aug. 25, 1965, 36,528/ 65 14 Claims. (Cl. 75-214) This invention relates to sparking plug electrodes and to tips for such electrodes and in this specification the term electrode is hereinafter used to include not only the whole sparking plug electrode but also a sparking tip for such an electrode.

The need for sparking plug electrodes to be made from a material which is resistant to deterioration at high temperatures and, in particular, to attack by the lead compounds which are added to petrol to reduce knocking, has long been appreciated.

Several prior proposals have been made to use certain of the platinum group metals either alone or alloyed with other metals for the manufacture of sparking plug electrodes. It has previously been proposed, for example, to manufacture a sparking plug electrode from ruthenium by powder metallurgical techniques and, thereafter, by cold working the resultant material to produce a fibrous microstructure. The degree of cold working suggested was such as to produce at least a 75% and generally a 90% reduction in cross-sectional area.

'Hitherto, it has been considered that a material having a fibrous microstructure was essential if the electrode was to have a relatively long working life. We have now found that sparking plug electrodes as herein defined which are strongly resistant to attack by lead and lead compounds at elevated temperatures, may be made from ruthenium powder or powder of an alloy of ruthenium and iridium by conventional powder metallurgical techniques without the resultant product having a fibrous microstructure, provided the powder comprises particles within the size range 1 to 76/1. (viz. the mesh size of a 200 ES. sieve) and with particles within the size ranges 10 -20 and 20/.L-30/L constituting respectively, 2035% and 30-50% by weight of the powder. By particle size in the above, we mean the diameter of the equivalent sphere as measured by the Coulter counting technique.

One method for producing a sparking plug electrode without a fibrous microstructure comprises the following steps:

(a) compressing a quantity of ruthenium powder or alloy powder having a particle distribution as referred to above, to form a powder compact whose density is from 54-68% of its theoretical maximum possible value;

(b) sintering the compact in an inert or reducing atmosphere at a temperature within the range 1500 C.- 1600 C.;

(c) repressing the sintered compact to increase its density by /2 to expressed as a percentage of the theoretical maximum possible value, and

(d) resintering the compact in an inert or reducing atmosphere at a temperature of from 1500 C.1600 C.

Preferably:

(i) the sintering and resintering of the compact in stages (b) and (d) above is carried out respectively for not less than 4 hours and not more than 4 hours and conveniently 2 hours;

(ii) the percentage by weight of the powder particles Within the size range -2Qu. is from 520% less than the percentage by weight of those within the size range 20-30 (iii) the particles within the size range 24-28;]. constitute from 10-25% by weight of the powder, and

(iv) those within the size range 14-18 i constitute from 1015% by weight of the powder.

One method of making a ruthenium pellet for use as a sparking tip for a sparking plug electrode will now be described by way of example.

A quantity of ruthenium or alloy powder having a particle size distribution such that the particles within the size ranges 1020,u, 20-30 24-28/L and I l-18a constituted respectively, 29.7%, 47.7%, 25% and 12.8% by weight of the powder, was dried in a circulating air oven for 2 hours at a temperature of 120 C. For this purpose, the powder was spread on a tray in the oven to a depth of not more than A.

A quantity of the dried powder was poured into the 0.092 diameter die of a pelleting press until it occupied a depth of about 0.250". The powder in the die was then subjected to a pressure of 50 tons per square inch to produce a compact 0.092" in diameter and 0.040" deep and having a density which was 67% of the theoretical maximum possible value.

The compressed powder compact so produced was then sintered in an atmosphere of cracked ammonia at 1550 C. for 16 hours to produce a sintered compact having a density which was 88% of the theoretical maximum possible value.

The sintered compact was next repressed at a pressure of tons per square inch at room temperature so as to increase its density, expressed as a percentage of the theoretical maximum possible density, from between 88% to 89 /2 Since it was found that the compressed powder compact shrank during sintering, the present step of repressing was carried out in a die 0.085" in diameter.

Finally, the sintered and repressed compact was resintered at a temperature of 1500 C. for 2 hours in an atmosphere of cracked ammonia.

The ruthenium pellet produced in the above way, which had a density amounting to 89% of the theoretical maximum possible value, was found to be highly resistant to the corrosive action of lead and lead compounds at elevated temperatures, and to be eminently suitable for use as the tip of a sparking plug electrode.

In order to assess the resistance of pellets in accordance with this invention to the corrosive action of lead, 5 such pellets, each 0.086" in diameter and ranging in length from 0.030 to 0.055", were placed with an excess of lead particles in a silica boat and heated in a cracked ammonia atmosphere at 900 C. for 2 hours, so that when the lead particles had melted, the pellets were totally immersed.

Thereafter, the molten lead was poured away and the ruthenium pellets were then heated and shaken together to remove any residual lead adhering to them. After this treatment, the pellets appeared to be clean, and showed no change in weight.

Finally, a microscopic examination of sections of the pellets revealed that the lead had in no way penetrated the pellets.

Although in the foregoing, particular reference has been made to the use of a ruthenium pellet manufactured using powder metallurgical techniques for sparking plug electrodes or tips thereof, we have also found that alloys of ruthenium and iridium may be used. As an example, 10% by weight of iridium powder was added to the starting powder and a highly satisfactory pellet obtained using the same techniques as described above.

In the accompanying drawings given by way of example:

FIGURE 1 illustrates an electrode according to the invention suitable for use as a central electrode.

FIGURE 2 illustrates an electrode according to the invention suitable for use as a side electrode,

FIGURE 3 illustrates an assembly including electrodes 1 and 2 in the form of ruthenium tips welded at 3 and 4 to support members 5 and 6 of conventional electrode material, and

FIGURE 4 illustrates an assembly similar to that of FIGURE 3.

What we claim is:

1. A method of making an electrode which is resistant to attack by lead and lead compounds at elevated terriperature comprising the steps of compressing a quantity of powder to form a powder compact whose density is from 54%-68% of its theoretical maximum value, the powder so compressed being selected from the group consisting of ruthenium and ruthenium-iridium alloy powders consisting essentially of particles within the size range of 1 to 76 with particles within the size range 10,1L20,LL and 20;r30a, constituting, respectively, 20% to 35% and 30% to 50% by weight of the powder with the 15% to 30% balance thereof consisting essentially of particles which are otherwise within said size range of 1 to 76 1, sintering the compact in an inert or reducing atmosphere at a temperature within the range 1500 C.- 1600 C., repressing the sintered compact to increase its density by /2% to 5% expressed as a percentage of the theoretical maximum possible value and resintering the compact in an inert or reducing atmosphere at a temperature of from 1500 C.1600 C.

2. A method according to claim 1 wherein the sintering and resintering of the compact is carried out respectively for not less than 4 hours and not more than 4 hours.

3. A method according to claim 1 wherein the sintering and resintering is carried out for 2 hours.

4. A method according to claim 1 wherein the percentage weight of the powder particles within the size range -20 is from 5*20% less than the percentage by weight of those particles within the size range 20-30 5. A method according to claim 1 wherein the particles within the size range 24-28 constitute from 10%25% by weight of the powder.

6. A method according to claim 1 wherein the particles within the size range 14718 constitute from 10% to 15% by weight of the powder.

7. A method of making an electrode in the form of a sparking tip according to claim 2 wherein the particle size distribution is such that the particle size within the ranges 10,u.20,u., 20/.4-30/L, 24g-28u and 14,u.18p. constitutes respectively 29.7%, 47.7%, 25% and 12.8% by weight of the powder.

8. A method according to claim 7 wherein the powder is before compressing dried in a circulating air oven for 2 hours at a temperature of 120 C.

9. A method according to claim 8 wherein for drying the powder is spread on a tray in the oven to a depth of not more than A (inch).

10. A method according to claim 9 wherein a quantity of the dried powder is poured into the 0.092 diameter die of a pelleting press until it occupies a depth of about 0.250".

11. A method according to claim 10 wherein the powder in the die is subjected to a pressure of tons per square inch to produce a compact 0.092" in diameter and 0.040" deep and having a density which is 67% of the theoretical maximum possible value.

12. A method according to claim 11 wherein the compressed powder compact so produced was then sintered in an atmosphere of cracked ammonia at 1550 C. for 16 hours to produce a sintered compact having a density which is 88% of the theoretical maximum possible value.

13. A method according to claim 12 wherein the sintered compact is next repressed at a pressure of 80 tons per square inch at room temperature so as to increase its density, expressed as a percentage of the theoretical maximum possible density, from between 88% to 89.5%.

14. A method according to claim 13 wherein the sintered and repressed compact is resintered at a temperature of 1500 C. for 2 hours in an atmosphere of cracked ammonia.

References Cited UNITED STATES PATENTS 3,108,000 10/1963 Cope 214 L. DEWAYNE RUTLEDGE, Primary Examiner.

A. J. STEINER, Assistant Examiner. 

1. A METHOD MAKING AN ELECTRODE WHICH IS RESISTANT TO ATTACK BY LEAD AND LEAD COMPOUNDS AT ELEVATE TEMPERATURE COMPRISING THE STEPS OF COMPRESSING A QUANTITY OF POWDER TO FORM A POWDER COMPACT WHOSE DENSITY IS FROM 54%-68% OF ITS THEORETICAL MAXIMUM VALUE, THE POWDER SO COMPRESSED BEING SELECTED FROM THE GROUP CONSISTING OF RUTHENIUM AND RUTHENIUM-IRIDIUM ALLOY POWDERS CONSISTING ESSENTIALLY OF PARTICLES WITHIN THE SIZE RANGE OF 1 TO 76$ WITH PARTICLES WITHIN THE SIZE RANGE 10$-20$ AND 20$-30$, CONSTITUTING, RESPECTIVELY, 20% TO 35% AND 30% TO 50% BY WEIGHT OF THE POWDER WITH THE 15% TO 30% BALANCE THEREOF CONSISTING ESSENTIALLY OF PARTICLES WHICH ARE OTHERWISE WITHIN SAID SIZE RANGE OF 1$ TO 76$, SINTERING THE COMPACT IN AN INERT OR REDUCING ATMOSPHERE AT A TEMPERATURE WITHIN THE RANGE 1500*C.1600*C., REPRESSING THE SINTERED COMPACT TO INCREASE ITS DENSITY BY 1/2% TO 5% EXPRESSED AS A PERCENTAGE OF THE THEORETICAL MAXIMUM POSSIBLE VALUE AND RESINTERING THE COMPACT IN AN INERT OR REDUCING ATMOSPHERE AT A TEMPERATURE OF FROM 1500*C.-1600*C. 